Toe cleanout and initial perforating in a horizontal well require two complete trips to be run into the well for the separate operations and involve large costs. For example, a horizontal wellbore “toe prep” service is performed with a coil tubing operation. In this toe prep service, coil tubing deploys a fluid-activated motor downhole. The motor turns a mill to cleanout the lower section of the wellbore casing of residual cement and the like. Once cleanout is done and the equipment removed, a subsequent descent of Tubing Conveyed Perforating (TCP) equipment is then used to perforate the casing to allow for pumping into the reservoir rock. This ultimately allows operators to perform conventional plug and perforation operations.
Tubing Conveyed Perforating (TCP) equipment is the most common type of equipment used for performing toe preparation of the casing. In the perforating operation, TCP equipment consisting of one to ten guns is conveyed downhole to prepare the toe of the wellbore casing with perforations. The TCP equipment, which is nonelectric, then establishes the first perforations in the casing and can be conveyed on coil tubing or on pipe.
In the pipe-conveyed operation, multiple pressure-activated firing heads of the TCP equipment are fired at the same time and may or may not have time delays attached. Pipe tally is used to correlate the position of the TCP equipment downhole in the casing, and a packer may or may not be run to isolate the annulus. In general, such an operation can have a total trip time from about 8 to 12 hours.
In the coil tubing-conveyed operation, one pressure-activated firing head or ball-drop-differential firing head fires first in the TCP equipment. Then, time delays between gun activations can allow the coil tubing to move the TCP equipment to different zones to be perforated. In the end, the number of guns that can be run and the different zones that can be perforated may be limited by the lubricator and crane equipment at surface. The depth recorded from the clean-out run with the coil tubing can be used to correlate the position of the TCP equipment downhole to the zones to be perforated. Overall, such an operation can have a total trip time from about 6 to 10 hours.
Rather than using perforations to prepare the toe, a sliding sleeve can be attached to the casing just above the toe shoe and can be cemented in place with the casing. To establish initial fluid communication, operations can circulate a ball to shift the sliding sleeve open. At this point, opens ports on the sleeve are then in contact with the formation to allow for fluid communication used in fracturing operations and the like.
Use of such a sliding sleeve removes the need for running coil tubing or using workover rigs, and the run time of such operations can be avoided. Still, use of such a sliding sleeve produces a limited number of holes at the toe. Pressure pumping is required to open the sleeves, and the initial preparation may need to be followed by wireline pump-down perforation operations.
Importantly, if the sleeve does not operate properly or if operations are unable to establish a sufficient pump rate, operators must perform traditional TCP toe preparation anyway. Besides, cementing the sleeve offers its own challenges as operations must limit the cement sheath at the sleeve and risk over displacing the cement.
Because the first operation after cementing is normally the cleanout run on coil tubing, it would be advantageous to combine toe-prep perforating with the clean-out run. However, combining these runs is not possible with conventional explosive perforating guns and equipment. Instead, combined runs of cleanout and toe-prep perforation can be done when sand jet perforation is used. In this technique, a mill and motor are run in the casing to drill-up any residual fill and cement in the casing. Then, operations uses high-pressure jets to direct an abrasive fluid slurry to abrade holes into the casing.
Sand jet perforation may not always be useful or possible for a given implementation. If the sand jet perforating tool does not operate properly or if a sufficient pump rate cannot be established, operations must perform traditional tubing conveyed perforating (TCP) toe-prep anyway. Besides, sand jet perforation may create a limited number of holes so that wireline (WL) pump-down perforating operations may still need to be performed afterwards.
In an attempt to overcome the problems with the above techniques, a toe gun has been developed that is attached to the outside of the casing. An example of such an external toe gun is the EXternal Toe Gun (EXTG) available from Smart Completions, Ltd. The external toe gun has TCP guns mounted to the outside of the casing just above the toe shoe and are cemented in place. The guns are actuated by pressuring up the casing and bursting a rupture disc. Once activated, the gun fires in two directions—into the casing to make a flow path and away from the casing into the formation to complete the flow path.
As will be appreciated, having an external toe gun outside the casing requires a larger borehole, which carries additional drilling costs and problems. The guns must also be run at the same time as the casing. Accordingly, the guns must remain downhole longer and can become damaged.
In the end, even this technique can produce a limited number of holes so that subsequent wireline pump-down perforation may need to be done. Finally, if a gun does not fire, traditional TCP toe prep must be performed anyway.
Wellbore isolation and re-perforating in an existing well also typically require two complete trips to be run into the well for the separate operations and involve large costs. For example, a rigless workover and re-perforation service is performed with a coil tubing operation. In this rigless workover service, coil tubing deploys a fluid-activated inflatable plug. The plug fills with fluid transmitted through the tubing and seals against the completion liner or casing to isolate the lower section from the remaining wellbore. Once isolation is achieved and the equipment removed, a subsequent descent of Tubing Conveyed Perforating (TCP) equipment is then used to perforate the casing to allow for pumping into and treating and/or extraction from the reservoir rock. This ultimately allows operators to perform rigless workover, recompletion operations.
The subject matter of the present disclosure is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.